Process of making castings of rare-earth metals and their alloys.



A. & M. HIRSCH.

PROCESS OF MAKING CASTLNGS 0F RARE EARTH METALS AND THEIR ALLOYS.

APPLICATION men SEPT. n. 1911. RENEWED NOV. 29. ms.

1,290,01 1 Patented Dec. 31, 1918..

A? 4 g W 15 A TTOR/VEY STATES PATENT OFFICE.

' ALCAN mason 41m MARX mason, on NEW' Yonx, N. Y., assroitons TO ALPHA rnonuc'rs comment, me, A CORPORATION or NEW YORK.

PROCESS OF MAKING CASTINGS 0F BARE-EART H'METALS AND THEIR ALLOYS.-

Specification of Letters Patent. Patented Dec, 31 1918-,

Application filed September 17, 1917, Serial No. 191,863. Renewed November 29, 1918. .Serlal No. 284,718.

To all whom it may concern Be it known that we, ALCAN Hmson and Manx Hinscii, itizens of the United States,

' and residents 0 New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Processes of Making Castings of Rare-Earth Metals and Their Alloys, of'

which the following is a specification.

The invention relates to improvements in the manufacture of castings of rare earth metals and their alloys and especially to the preparation of the metals for casting. The

improvements are particularly adapted to the manufacture of castings of alloys of cerium or lanthanum for sparking purposes.

Prior to the present invention it has been considered extremely diflicult to cast the desired rods and shapes of cerium and its alloys because of. the extreme infiammability of the metal on the one hand and its great tendency tochemical reaction with carbon and other substances and to alloying with metals on the other hand. It was only by the laborious and wasteful process of sawing or turning beneath the surface of oil, or while constantlydrenching the fresh surfaces and cuttings with oil, that it wasgenerally known how to make the small commercial shapes necessary for use in lighters, ignition fiints, etc.

The present process has for its object the providing of improvements whereby the rare earth metals and their alloys may be satisfactorily cast in the various forms desired in commerce and, in many cases,,with

suflicient exactitude of size to avoid the ne- 'cessity of machining, thereby avoiding not only delay and expense, but'much loss of material, which, once powdered, is .extremely difficult to recover in usable shape. Also, according to the present invention, the

cast metal or alloy is obtained in a most simple and economical manner and substantially free from ob ectionable impurities.

Further and more specific objects, features and advantages will more clearly appear from the detailed description given below, taken in connection with the accompanying sheet of drawings, which forms a par-t of this, specification.

In the drawing,

Figurel is a vertical section. of a pre-. ferred form of apparatus for melting the metals;

Fig. 2 is a top view of a mold into which the molten metal may be poured for casting; Fig. 3 is a vertical section taken.on' the line 3 3 of Fig. 2; Fig. 4 is a vertical section taken on the line 44 of Fig. 2

Fig. 5 is a to modified form 0 mold; and

Fig. 6 is a similar view illustrating still another form of mold.

As an illustrative example of the improve ments, the preferred process for the manufacture of castings of an alloy of cerium, lanthanum, didymium, etc., and iron will be described.

Large pigs of an alloy of cerium, lanthanum and didymium, and possibly small quantities of erbium and thorium, etc,', and containing more or less impurities, are broken up, as with a hammer, into pieces about one inch in diameter. It is preferred to avoid using much smaller pieces than one-half inch in diameter, as they tend to thicken the melt into which they are later put, probably because of the greater amount of oxid formed on the surfaces of the'pieces when an equal weight of smaller pieces is used. Larger pieces may be used, especially,

plan view illustrating a cover surrounding the top of the crucible and resting on the jacket 4. Other forms of apparatus may, however, be used.

After the barium chlorid has been fused in the crucible and the water contained in the barium chlorid crystals has been evolved and the mass reached a quiet state of fusion,

the pieces of metal, consisting mostly of cerium with some lanthanum and small quantities of other metals, are washed in kerosene or other suitable oil to remove dirt, oxids and carbids that may be on the sur-.

face thereof, and then: they are partially dried, as with news print paper, and then the pieces of metal are added to the melt of barium chloridin fairly large batches, that is to say, as many pieces are added at a time as can be readily shoved under the surface of the barium chlorid. Any kerosene or other oil remaining on the piecesburns off as they go into the molten barium chlorid. The mass should not be stirred, and in adding the metal the melt should be agitated as little as possible. The cerium metal or alloy added should preferably be low in iron, as metal high in iron not only has a higher melting point, but is apt to contain more of other impurities and these impurities are then far more diflicult to separate. We, therefore, prefer to use a rare earth metal containing about 10% or less of iron. When the metal added has become fluid at the bottom of the crucible, another batch of metal may be added in the same way and the molten metal batch built up, care being taken not to expose the already molten cerium metal in the melt; to the air, which would rapidly ignite or oxidize it. The

heating of the pieces of metal to melt them should be carried out relatively quickly, because, if the operation is carried out slowly, the metal melt does not become as clear and homogeneous, the fused salt above it be comes more viscous and diilicult to separate from the metal, and much metal is apt to be lost, nor does the metal pour so Well when it is later poured from the crucible. By

. relatively quickly, we mean that the whole operation of melting, alloying and casting the metal should take not over about two hours, instead of several hours.

When the crucible is about one-half .full of molten metal, as illustrated at 6 in Fig. 1, any other metal which it is desired to alloy with it is added. Inmost cases, it is desirable to add certain other metals, such as iron,

' to harden the resulting alloy. This is added in the form of soft wrought iron wire. It is first cut off in pieces weighing, say, 40 to, grams and the pieces wound into loose coils or spools. These coils of wire are poked into the melt under the layer 7 of barium.

' chlorid. If ironalone is used, it is preferred to add sufficient iron so that the resulting alloy contains about 30% of iron. The iron is preferably added periodically in about tinued until they are all melted into the alloy. Before the addition of any subsequent batch of iron, the previous batch of iron should be thoroughly absorbed. During the addition of the iron, care should be taken not Leeann increases the fluidity of the molten metal.

surface of the melt and keeps the rest of the batch out of contact with the air. When the melt is .fairly liquid, andabout ten minutes before it is poured out, it is thoroughly, but gently, stirred to produce a. homogeneous mass. It is important to increase the fiuidit in order that, when poured into the mol s the molten metal will not be congealed prematurely as more clearly pointed out hereinafter.

When the metal is thoroughly molten and homogeneous, the crucible is lifted out of the furnace and a hole poked through the crust, if any, of barium chlorid adjacent the side of the crucible, by means of'a hot, thin iron bar or rod. The molten metal is then poured through this hole out into suitable molds. It is desirable to make up melts of metal of over 350 grams, preferably about.23 kilograms, as, if smaller melts, say of 200 grams, are used, difficulty is encountered in pouring the metal.

While any form of molds may be ISQCl, it is preferred to make them of iron. However, graphite and other materialsmay be used for A layer of hardened chlorid forms on the.

the molds. The mold, especially if made of the metal at a temperature so near to the solidifying point that excessive burning is avoided and at the same time permits this metal, near to the point of congelation, to

find its way into andfill the mold. The mold I should be slowly and uniformly heated to prevent Warping thereof; Bythus'heating the metal mold the residual heat absorbing capacity of the mold, up to the temperature ofcongelation of the molten metal is reduced to a point where it does not materially affect the homogeneity of the resulting casting by causing cracks and breaks in the casting caused by rapid and uneven cooling of metal mold a thin sheet metal mold having little heat absorbing capacity may be used to accomplish the same result as will, be readily apparent to those skilled in the art. In Figs. 2, 3 and 4, there is illustrated an iron mold composed of two partslO and 1.1, the part 10 the molten metal. This may be accomplished, in other ways. Instead of "heating a heavy four angle 'bars 14 running along near the top and bottom on the outside of the plates appears"-lt0m Figs. 2 to (;-the resulting cast ings have relatively great-length and the ratio between the volume of the casting and the area of the molding surface from which.

withdrawal of heat may take place is less than the ratio of 1 cubic inch of metal to 15. square inches of molding surface. In order that this relatively large heat withdrawal surface may not cause. premature congelation in the mold and prevent the complete flow of molten metal into the mold, the chilling capacity of the noldis reduced as above described and the fluidity of the molten metal is increased prior to pouring by stirring and by a slight increase inthe temperature thereof, as above described.

. Before pouring the metal into the mold, the surfaces of the mold are dusted or otherwise coated with a layer of magnesia or other finely-divided inert material, so .that the pieces of cast-metal may be easily removed from the mold. The metal is poured into the connecting slot 13 and runs into '25 the mold slots 12, filling them up. Themold should be allowed to cool slowly, that is, no

ing, but the old is allowed to air cool, and

- artificial meals are used to hasten the coolif the coating. of magnesia has been uniform,

a slight tapping of the plate 11, after plate 10 has been removed therefrom, should so loosen the pieces of cast metal that they may be easily removed.

In Fig. 5 is shown a top view of a similar mold adapted to form cylindrical-shaped castings or sticks of metal, and in Fi' 6 is shown a top view of a similar mold a apted to caststicks of metal rectangular in acrosssection. The resulting cast sticks of metal. as.

they come from the'molds shown in Figs. 2 to 6 are especially adapted for sparking purposes and differ materially fromthe pieces of alloy heretofore used for this purpose and which were made by sawing or turning under oil. The alloy castings made according to our process, have matt unsmeared glassy surfaces where formed adjacent the metal mold surfaces. While the surfaces may be somewhatrough owing to the presence of some air or blow holes on the surface, yet the surfaces have a characteristic glassy appearance and the metal is not smeared over as is the ;case when the ieces are. formed by sawing or turning.

oreover, especially when cast in the metal molds,.it is found that the castings. at said surfaces have a superficial skin composed of the alloy, but poorer in the rare earth metal than is. the alloy in the interior of the'cast piece. This probably is due to the alloy taking up metal or particles from metal mold surface. This skin serves as asubstantially non-corrosive coating or layer while having the necessary sparking properties. By melting and pourin the alloyed metals from beneath a fused sa t as above described flakes of oxid, which would otherwise be present in the casting are substantially eliminated and the'resultant casting is .extremely homogeneous. I

In many cases, it is found' that crude metal (chiefly cerium or lanthanum), as taken from the electrolytic cell in'which it is produced, is so 'im ure or non-homogene-- ous that a stable an sufliciently air-resistant alloy is not produced by a single fusion of the crude metal under the purifying bath, as of barium chlorid. ,In such case, it is desirable to make two or more successive fusions as described, referably before alloying (raising the me ting point) and casting into final shapes (se arating the metal or 'alloy into small pieces After, each such prelimlnary purifying fusion, the slag or fused salt may be removed from the crucible and freshpurifying salt already-dehydrated added to the metal therein, or the metal may be cast into pi *of convenient size (about 1x1x4 inches) or remelting or for breaking into lumps for remelting.

'While it has been suggested that in the alloys, the metal may be melted below a making of certain brass, bronze and steel 1 layer of borax or waterglass, this is a very difl'erent proposition from-the making of castmgs of the rare earth metals, such as v cerium or lanthanum, and their yrophoric alloys. Cerium is not only readi y oxidized when heated, but rapidly i ites, and, furthermore, has such a great a nity for oxygen that if melted below such slags' as borax or waterglass, would so rapidly combine with the oxygen therein as to cause a violent reaction. With the brass, bronze and steel alloys, there is no such problem. The making of bronze, brass and steel alloys is anart 1 distinct and separate from the art of making pyrophoric alloys of cerium and similar rare earth metals in which the metals are so chemically active that they even unite readily with carbon to form carbid.

It has also been suggested that alloys can be prepared by me ting together certain quantities of a rare earth metal and aluminum under a covering layer of sodium chlorid and potassium chlorid, but unless certain additional features or precautions ,are employed in the process,'the results are very unsatisfactory and even then barium chlorid has distinct advantages not possessed by a mixture of sodium chlorid and potas sium chlorid.

Instead of using barium chlorid as a proiso ' loss of the salt, but great inconvenience to the workmen results. Furthermore, it is believed that the surface tension of fused cerium and. its alloys against a molten bath high in barium ohlorid is far more advantageous to making homogeneous castings and protecting the surface of the metal from too rapid oxidation. Copper or magnesium may also be added to the molten metal to I ing the rare earth metal-below a layer of a harden the resulting alloy, or increase the fatness and heat of the spark, Other methods preventing oxidation of the melt may L The process of making castings of cerium and similar rare earth metals and their alloys, which consists in melting the rare earth metal under a layer of molten barium chlorid to protect the molten metal from oxidation or ignition and pouring the molten metal into molds.

.2. In the process of makin castings of cerium and similar rare cart metals and their alloys, the steps which consist inmeltmolten salt inert to the rare earth metal and protecting the molten metal from oxldatlon,

and then introducing an alloying metal into the molten rare earth metal through the layer of'protecting salt.

3. In the process of making castings of cerium and similar rare earth metals and their alloys, the steps which consist in melting the rare earth metal below alayer of a molten salt inert to the rare earth metal protecting the molten metal from oxidation, and introducing an alloying metal and melt ing the same with the rare'earthmetal and then stirring the melt and raising the temperatureof the melt'to increase the fluidity thereof: before pouring.

4. In the process of makingcastings of cerium and similar rare earth metals and their alloys, the steps which consist in melting a protecting salt inert to the 'rare,

earth metal in a suitable vessel and introducing the rare earth metal in the form of pieces about one-half inch in diameter or larger into the molten salt and below the surface thereof, causing therare earth metal to melt and fall to the bottom of the bath.

5. The process of making castings of co rium and similar rare earth metals and their alloys which consists in melting a protecting salt inert to molten cerium and lanthanum, in a suitable vessel and introducing the rare earth metal into the molten salt and below the surface thereof, causing naec o'iii the rare earth. metal to melt and fall to the bottom of "the bath.

6. In the process of making castings of' cerium and similar rare earth metals and their alloys the steps which consist in preparing pieces of the rare earth metal, wash ing oxide and dirt'f'roni the surfaces thereof with volatile organic liquid, melting" a layer of a protecting salt inert to the rare earth metal, and introducing the washed pieces into the molten salt and below'the surface thereof, causing the rare earth metal to melt and fall to the bottom of the batch.

7. In the process of making castings of alloys of cerium or lanthanum the steps which consist in melting rare mailman containing mainly cerium or lanthanum and containing about 10% or less of iron, below a layer of molten salt inert to cerium and after the rare earth metal containing about 10% or less of iron is melted,-then adding thereto an alloying metal to harden th resulting alloy.-

8. In the process of making castings of alloys of cerium or lanthanum, the steps which consist in melting rare earth metal contalning mainly cerium or lanthanum beheath a layer of molten salt inert to cerium,

and adding thereto iron in the form of iron wire.

loys of cerium or lanthanum. which consists in :meltmg rare earth metal containing mainl cerlum or lanthanum beneath a layer of mo ten salt inert to cerium, the resulting melt of metal being about 350 grams or over,- and pouring the molten metal to be cast.

10. In the process of making castings of 9. The process of making castings of a1- cerium'and similar rare, earth metals and 1 their alloys, the steps which consist in purifying and consolidating the metal by re' peated fusion with a purifying bath. of

fused salt inert to the rare earth metal;

11. In the process of making castings of cerium and similar, rare earth metals and their alloys, the steps which consist in puri;

fying and consolidating the metal by repeated fusion with a purifying "bath containingfused barium chlorid.

12. In the rocess of making castings of cerium and similar rare earth metals and their alloys, the steps which consist in melting and dehydrating a salt which is inert to. I

the rareearth metal, introducing lumps of the rare earth metal into and below the surface of the molten salt, and melting the-rare earth metal below said surface.

13. In the process: of making castings of cerium and similar rare earth metals and their alloys, the steps which consist inmelting and dehydrating a salt which is inert to the rare earth metal, introducing lumps of ,v

therare earth metal into and below the surface of the molten salt, and melting the rare 1 metal to be cast below thesurface 0 earth metal below said surface, and theninw troducing an alloying metal through said surface and melting the alloyin metal beneath said surface to form an alloy thereof with the rare earth metal.

14. In th process of making castings of cerium and similar rare earth metals, the step which consists in melting thecrude metal below a layer of molten salt inert to the rare earth metal to segregate impurities from the molten metal.

15. In the process of making casting of pyrophoric alloys of cerium and similar rare earth metals, the steps whichconsist in first preparing the metal for alloying, by fusion beneath the surface of a fused salt inert to the metal and capable of segregating impurities therefrom, and then refusing the metal under a fresh batch of fused salt and adding an alloying metal to the fused metal.

16. In the process of making castings of ceriu-m and similar rare earth metals and their alloys, the steps which consist in melting a salt which is inert to the molten rare earth metal or alloy thereof, meltin the said fused salt, pouring the -molten metal into molds to form castings in which the ratio between the volume of cast molten metal and the area of the molding surface from which radiation of heat may take place is in the ratio of 1 cubic inch of metal to 15 square inches or less of molding surface, and. raising the temperature of the molten metal before casting to increase the fluidity of the molten metal, whereby the large heat Withdrawing surface for the molten metal in the mold, will not prevent flow of molten metal into the mold by premature congelation of 40 the metal.

17. The new article of manufacture comprising a cast piece of an alloy of cerium or lanthanum, and a hardening metal, adapted for sparking purposes and havin matt unsmeared glassy surfaces where ormed adjacent the casting mold, the casting at said surfaces having a superficial skin composed of the alloy but poorer in rare earth metal than the alloy in the interior of thecast piece, said skin serving as a substantially non-corrosive coating or layer while having the necessary sparking properties, said casting bein substantially free from flakes of oxid an substantially homogeneous.

Signed at New York in the county of vNew York and State of New York this 15" day of September A. D. 1917.

ALGA-N HIRSC'H.

MARX HIRSCH.

Witnesses:

JAMES N. TIMMERMANN, "GoRHAM CRosBY. v

the interior of the casting being l 

